Atomization by Acoustic Levitation Facilitates Contactless Microdroplet Reactions

Microdroplet chemistry is now well-known to be able to remarkably accelerate otherwise slow reactions and trigger otherwise impossible reactions. The uniqueness of the microdroplet is attributable to either the air–water interface or solid–liquid interface, depending on the medium that the microdroplet is in contact with. To date, the importance of the solid–liquid interface might have been confirmed, but the contribution from the air–water interface seems to be elusive due to the lack of method for generating contactless microdroplets. In this study, we used a droplet atomization method with acoustic levitation. Upon manipulation of the acoustic field, the levitated parent droplet can be further atomized into progeny microdroplets. With this method, only the air–water interface was present, and a large variety of reactions were successfully tested. We anticipate that this study can be an advance toward the understanding of the air–water interfacial processes of microdroplet chemistry.